Surface inspection method and surface inspection apparatus

ABSTRACT

A surface inspection apparatus capable of acquiring scattered light intensity distribution information for each scattering azimuth angle, and detecting foreign matters and defects with high sensitivity. A concave mirror for condensation and another concave mirror for image formation are used to cope with a broad cubic angle. Since mirrors for condensation and image formation are used, a support for clamping the periphery of a lens is unnecessary, and an effective aperture area does not decrease. A plurality of azimuth-wise detection optical systems is disposed and reflected light at all azimuths can be detected by burying the entire periphery without calling for specific lens polishing. A light signal unification unit sums digital data from a particular system corresponding to a scattering azimuth designated in advance in the systems for improving an S/N ratio.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a surface inspection method, and an apparatusfor the method, for inspecting fine foreign matters and defects on asemiconductor substrate (semiconductor wafer).

2. Description of the Related Art

Defect inspection for inspecting foreign matters adhering to a surfaceof a semiconductor substrate (semiconductor wafer) and scratchesoccurring during processing has been carried out in a fabrication lineof the semiconductor substrate to monitor a occurrence state of dust inproduction setup. In a semiconductor substrate before the formation of acircuit pattern, for example, fine foreign matters and defects of belowdozens of nm must be detected.

In the inspection of the surface of the semiconductor substrate, crystaldefects existing in a shallow region in the proximity of the substratesurface and surface coarseness of the substrate surface are also theinspection objects besides the foreign matters and defects.

A customary technology for detecting foreign defects on the surface ofthe inspection object such as the semiconductor substrate is describedin U.S. Pat. No. 5,798,829, for example. This technology fixedlyirradiates a condensed laser luminous flux to the surface of thesemiconductor substrate, detects scattered light occurring from foreignmatters adhering to the semiconductor substrate and inspects the foreignmatters and the defects of the entire surface of the semiconductorsubstrate through rotation and parallel movement of the semiconductorsubstrate.

A concave mirror using a rotary elliptic surface as a reflecting surfaceis used for detecting scattered light. The detection position on thesemiconductor substrate is set to the first focal point of the ellipsisand a light reception surface of a light reception device is set to thesecond focal point so that scattered light occurring from the foreignmatter can be condensed at a broad cubic angle and fine foreign matterscan be detected, too. In this way, the prior art technology does notazimuth-wise isolate and detect scattered light emitted from the foreignmatter and defect in all the azimuth directions but collectivelycondenses and detects the scattered light.

On the other hand, JP-A-2001-255278 discloses a technology that arrangescondenser lenses and optical detectors in directions of a plurality ofazimuth angles with respect to the surface of a semiconductor substrateand detects scattered light condensed by the condenser lens by anoptical detector in accordance with a scattering azimuth. Thistechnology can carry out detection in an advantageous azimuth directionin match with radial direction distribution characteristic of thescattered light from the fine foreign matter.

The technology described in JP-A-2002-188999 detects scattered lightfrom a surface of a semiconductor substrate from all azimuth directionsby using one parabolic surface mirror with respect to the surface of thesemiconductor substrate.

SUMMARY OF THE INVENTION

However, the surface inspection apparatus of the first patent referencedescribed above that uses the reflecting mirror has the following meritsand demerits in comparison with a surface inspection apparatus thatisolates, condenses and detects the scattered light from foreign mattersand defects in a plurality of azimuth direction by using a condenserlens.

The first merit is that the concave mirror has no break in the azimuthdirection (a direction having an axis of symmetry with respect to thenormal of the surface of the semiconductor wafer) and continuously bearsa condensation operation. From the aspect of a light reception cubicangle, therefore, the concave mirror has no dead angle but has highcondensation efficiency.

The second merits resides in that the concave mirror can be supportedfrom the back side by, for example, bonding and fixing a supportstructure to the back side (not a reflecting surface) and does nothinder condensation efficiency on the reflecting surface side that bearsthe condensation operation.

The third merit is as follows. Since the foreign matter and defect aredetected by condensing and detecting scattered light occurring within arelatively narrow range of the angle of elevation by using one opticaldetector, the number of photons that are incident into one opticaldetector can be advantageously secured. Particularly, when the foreignmatter and defect as the detection object is extremely small and theresulting total scattered light quantity is markedly small, asatisfactory S/N ratio can be secured.

On the other hand, the first demerit is that scattered light intensitydistribution information cannot be obtained for each scattering azimuthdirection and classification capacity of the detected foreign matter anddefect is inferior.

The second demerit is that since only background scattered light thatbecomes noise from an azimuth direction in which scattered light fromthe foreign matter and defect is weak is summed for those foreignmatters and defects which have strong scattered light distribution in aspecific azimuth direction, the S/N ratio is not satisfactory.

The surface inspection apparatus described in the second patentreference that uses a plurality of condenser lenses has the followingmerits and demerits in comparison with the surface inspection apparatusthat collectively condenses scattered light from the foreign matters anddefects by using one concave mirror using a rotary elliptic surface as areflecting surface.

The first merit is that classification capacity of the detected foreignmatter and defect is high because scattered light intensity distributioninformation for each scattering azimuth angle can be acquired.

The second merit is as follows. It is possible not to pick up only thosebackground scattered light which may result in the noise in the azimuthdirection in which scattered light is weak for the foreign matter anddefect having a strong scattered light distribution in only a specificazimuth direction. (It is advisable not to use a signal in such anazimuth direction). This is advantageous in the aspect of the S/N ratio.

On the other hand, the first demerit is as follows. Because the range ofan azimuth angle of 360 degrees of the entire periphery having asubstantially equal angle of elevation must be covered with a pluralityof lens incidence surfaces, a plurality of lenses are arranged inalignment on the circumference that has a predetermined radius. To burythe entire periphery without gaps, the shape of the incidence surface ofthe individual lens must be polished into a shape approximate to arectangle or a trapezoid.

The second demerit is that a frame-like support structure is necessaryfor clamping and holding the lenses from their periphery and theeffective aperture area bearing the condensation operation becomessmaller as much.

The third demerit is that when the foreign matter and defect as thedetection object is extremely small and the resulting total scatteredlight quantity is markedly small, the number of photons incident intoone optical detector decreases extremely when the total scattered lightquantity is divided into a plurality of azimuths. This isdisadvantageous from the aspect of the S/N ratio.

The technology described in the third patent reference mentioned aboveinvolves the problem that the S/N ratio drops when the foreign matterand defect as the inspection object is extremely small and the resultingscattered light quantity is markedly small.

The surface inspection apparatus in the latest semiconductor devicefabrication process is required to be capable of detecting andclassifying a greater number of kinds of foreign matters and defects asthe minimum detection grain size of the foreign matters and defects hasbecome smaller.

To satisfy such a requirement, a condensation optical system capable ofconducting detection in a plurality of azimuths and improving detectionsensitivity has been required.

It is an object of the invention to accomplish a surface inspectionmethod and a surface inspection apparatus each being capable ofacquiring scattered light intensity distribution information for eachscattering azimuth and detecting foreign matters and defects with highsensitivity.

To accomplish the object, the invention employs the followingconstruction.

A surface inspection method according to the invention irradiates lightto a predetermined position on a surface of an inspection object to forman illumination spot, detects light that is scattered, diffracted andreflected from the illumination spot and detects foreign matters anddefects existing on the surface of the inspection object or in theproximity of, and inside, the surface on the basis of light detected.

The light scattered, diffracted and reflected from the illumination spotis condensed and reflected by a plurality of concave mirrors forcondensation that are arranged for each of a plurality of azimuth angleswith respect to the surface of the inspection object, reflects lightreflected from the condensation concave mirrors arranged at the sameazimuth angle by concave mirrors for image formation that are arrangedat a higher angle of elevation than the condensation concave mirrorswith respect to the surface of the inspection object, distinguishes anddetects the light reflected from the plurality of image formationconcave mirrors, respectively at a detection device, and detects theforeign matters and defects existing on the surface of the inspectionobject or in the proximity of, and inside, the surface on the basis ofthe light detected.

A surface inspection apparatus according to the invention includes aninspection object movement stage on which an inspection object is putand which moves the inspection object, illumination device thatirradiates light to a predetermined position on a surface of theinspection object and forming an illumination spot, and detection devicethat detects light scattered, diffracted and reflected from theillumination spot, and detects the foreign matters and defects existingon the surface of the inspection object or in the proximity of, andinside, the surface on the basis of light detected by the detectiondevice.

The surface inspection apparatus further includes a plurality ofcondensation concave mirrors arranged at a plurality of azimuth angles,respectively, with respect to the surface of the inspection object, andcondensing and reflecting light scattered, diffracted and reflected fromthe illumination spot; image formation concave mirrors arranged at ahigher angle of elevation than the condensation concave mirror withrespect to the surface of the inspection object at each of the pluralityof azimuth angles, and reflecting light reflected from the condensationconcave mirrors arranged at the same azimuth angles; another detectiondevice that distinguishes and detects each of the rays of lightreflected by the plurality of image formation mirrors; and foreignmatter/defect classification device that detects the foreign matters anddefects existing on the surface of the inspection object or in theproximity of, and inside, the surface on the basis of light detected bythe detection device.

The invention can accomplish a surface inspection method, and anapparatus for the method, each capable of acquiring scattered lightintensity distribution information for each scattering azimuth anddetecting foreign matters and defects with high sensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view of a surface inspection apparatusfor executing a surface inspection method according to a firstembodiment of the present invention;

FIG. 2 is an explanatory view useful for explaining an illumination spotin the first embodiment of the invention;

FIG. 3 is an explanatory view useful for explaining an azimuth-wisedetection optical system in the first embodiment of the invention;

FIG. 4 is an explanatory view useful for explaining an arrangement ofoptical detectors in the first embodiment of the invention;

FIGS. 5A to 5C are explanatory views each useful for explaining aconcave mirror for condensation in the first embodiment of theinvention;

FIG. 6 is an explanatory view useful for explaining another arrangementof the optical detectors in the first embodiment of the invention;

FIG. 7 is an explanatory view useful for explaining acondensation/detection optical system of a surface inspection apparatusaccording to a second embodiment of the invention;

FIG. 8 is an explanatory view useful for explaining the formation of anillumination spot in the second embodiment of the invention; and

FIG. 9 is a schematic structural view of a surface inspection apparatusfor executing a surface inspection method according to the secondembodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the invention will be hereinafter explainedwith reference to the accompanying drawings.

FIG. 1 is a schematic structural view of a surface inspection apparatusfor executing a surface inspection method according to a firstembodiment of the present invention. In the drawing, a semiconductorwafer 100 as an inspection object is shown adsorbed by vacuum to a chuck101. The chuck 101 is mounted onto an inspection object movement stage102 having a rotation stage 103, a parallel movement stage 104 and a Zstage 105.

An illumination optical system 110 and a scattered/diffracted/reflectedlight detection optical system 150 are arranged above the semiconductorwafer 100. A pulse laser that causes time-wise repeatedly pulseoscillation of light of a wavelength of the ultraviolet region is usedfor a light source 11. An illumination beam 21 outgoing from the lightsource 11 forms an illumination spot 3 shown in FIG. 2 owing to theoperation of an illumination lens 18. To detect highly precisely fineforeign matters and defects, an angle of elevation of the illuminationbeam 21 to the surface of the inspection object is a low angle ofelevation of about 5 to about 25 degrees, more preferably an angle inthe proximity of the Brewster angle with respect to the materialconstituting the inspection object, such as crystalline Si (silicon).

In the first embodiment of the invention, therefore, the illuminationbeam 21 is allowed to be incident obliquely at an angle of about 13degrees. For this reason, the illumination spot 3 has a substantiallyelliptic shape. The polarization state of the illumination beam 21 iscontrolled to “P polarization” or “S polarization” or “circularpolarization” or “elliptic polarization”.

Scattered/diffracted/reflected light generated from the illuminationspot 3 is condensed and detected by the scattered/diffracted/reflectedlight detection optical system 150. The scattered/diffracted/reflectedlight detection optical system 150 has six azimuth-wise detectionoptical systems 160 the detection direction angles of which are spacedapart from one another by about 60 degrees so that the componentsscattered, diffracted and reflected in directions of left front/rightfront/left side/right side/left back/right back among thescattered/diffracted/reflected light generated from the illuminationspot 3 by the illumination beam 21 can be isolated and detectedindividually.

FIG. 3 is a schematic structural view of each azimuth-wise detectionoptical system 160. As described above, the concave mirror using arotary elliptic surface as a reflecting surface can condense lightemission dispersed in a broad cubic angle range from near a first focalpoint by only a single reflecting surface but cannot form images of twolight emission points existing in the proximity of the first focal pointas separate images of two points in the proximity of a second focalpoint. A combination of at least two secondary curved surface concavemirrors is necessary to constitute an optical system having an imageformation capacity while suppressing spherical aberration andastigmatism by only a reflecting mirror using its secondary curvedsurface as a reflecting surface.

Combinations of a rotary double curved surface+rotary double curvedsurface, rotary curved surface+rotary elliptic surface and rotary doublecurved surface+paraboloid of revolution have already been put intopractical application in the field of astronomical microscopes usingvisible rays and X rays but a cubic angle range capable of condensationis narrow. Scattered light scattering in a broad cubic angle fromforeign matters and defects must be received in optical surfaceinspection, and the condensation cubic angle capable of being achievedby the combinations described above has not been entirely satisfactory.The combination of the paraboloid of revolution+paraboloid of revolutionis one of the combinations capable of coping with a broad cubic angleamong the combinations for achieving the image formation capacity by twosecondary curved surface concave mirrors.

In the first embodiment of the invention, therefore, the azimuth-wisedetection optical system 160 includes a concave mirror 161 forcondensation that uses a part of its paraboloid of revolution as areflecting surface and a concave mirror 163 for image formation thatuses a part of its paraboloid of revolution as a reflecting surface. Theparaboloid of revolution of the reflecting surface of the condensationconcave mirror 161 and the paraboloid of revolution of the reflectingsurface of the image formation concave mirror 163 have a common opticalaxis 165. The common optical axis 165 is inclined outward by about 5degrees to the normal 167 of the surface of the inspection object in thedetection direction to which the azimuth-wise detection optical system160 corresponds, as shown in FIG. 3.

The focus 162 of the paraboloid of revolution of the reflecting surfaceof the condensation concave mirror 161 is arranged substantially inconformity with the center of the illumination spot 3 on the surface ofthe inspection object and the focus 164 of the paraboloid of revolutionof the reflecting surface of the condensation concave mirror 163 isarranged substantially in conformity with the center of the lightreception surface of the optical detector 7. The focal length of thecondensation concave mirror 161 is set to be substantially equal to thatof the image formation concave mirror 163.

In the arrangement described above, the scattered/diffracted/reflectedlight occurring from the illumination spot 3 is converted to a parallelpencil of rays 166 by the condensation concave mirror 161 and these raysare incident into the image formation concave mirror 163. The imageformation concave mirror 163 forms the image of the parallel pencil ofrays 166 on the optical detector 7 as the focal surface and forms theimage that is substantially a multiple of the illumination spot. In thefirst embodiment of the invention, the distance from the focus 162 ofthe condensation concave mirror 161 to the focus 164 of the imageformation concave mirror 163, that is to say, the distance from thecenter of the illumination spot 3 to the center of the light receptionsurface of the optical detector 3, is set to about 200 mm.

Therefore, when the common optical axis 165 of the condensation concavemirror 161 and the image formation concave mirror 165 is inclined byabout 5 degrees to the normal 167 of the surface of the inspectionobject, the gap between the images of the adjacent measurement spots 3corresponds to the length of one side of an equilateral hexagoninscribed in a circle the radius of which satisfies the relation 200mm×sin 5°=approx. 17.4 mm (formula 1). Therefore, the gap between theimages of the adjacent measurement spots 3, too, is 17.4 mm and theillumination spot image formed by each of the six azimuth-wise detectionoptical systems 160 does not spatially interfere with one another butcan be isolated and detected by the independent optical detector 7 thatis disposed for each azimuth-wise detection optical system.

As shown in FIG. 5A, six, in total, of condensation concave mirrors 161of the six azimuth-wise detection optical systems 160 are produced bysplitting one rotary elliptic surface mirror into six units. The outershape of the reflecting surface of each condensation concave mirror 161is such as shown in FIG. 5B. Four condensation concave mirrors 161, thatis, the left front/right front/left back/right back concave mirrors,have a small semi-spherical notch portion 300 to avoid the illuminationbeam 21 and the optical path of the regular reflected light of theillumination beam 21. These six condensation concave mirrors 161 arearranged in such a fashion that the gap between the adjacent pair ofcondensation concave mirrors 161 becomes small as shown in FIG. 5C.

As described above, in the first embodiment of the invention, the angleof elevation of irradiation of the illumination beam 21 is set to 13degrees. It is known that in the case of foreign matters satisfying theRayleigh scattering rule, scattered light from the foreign mattersmostly occurs within the range of the angle of elevation of about 7 toabout 50 degrees.

The arrangement according to the first embodiment of the invention canefficiently condense and detect those types of light which arescattered, diffracted and reflected within the range of the angle ofelevation of about 7 to about 50 degrees among the scattered, diffractedand reflected light occurring from the illumination spot 3.

When the foreign matter 1 passes by the illumination spot 3 in theconstruction described above, the scattered/diffracted/reflected signalcan be obtained from the optical detector corresponding to eachazimuth-wise detection optical system 160. The first embodiment of theinvention uses a photomultiplier for the optical detector 7 but opticaldetectors based on other detection principles may be used, too, as longas they can detect with high sensitivity thescattered/diffracted/reflected light from the foreign matter.

The scattered/diffracted/reflected light signal from each opticaldetector is amplified by the amplifier 26 disposed for each opticaldetector 7, is sampled in a predetermined sampling cycle dT and isconverted to digital data by an A/D converter 30. The group of thedigital data acquired in such a fashion as to correspond to eachazimuth-wise detection optical system 160 is sent to ascattered/diffracted/reflected signal unification unit 200. Thescattered/diffracted/reflected signal unification unit 200 sums thedigital data from the azimuth-wise detection optical system 160corresponding to a predetermined scattering direction and can thusaccomplish data processing for acquiring unified digital data having anS/N ratio which is much more improved than an S/N ratio obtained by themere addition of the digital data. Weighted linear coupling may be usedfor the synthetic algorithm of these digital data.

The unified digital data obtained by the scattered/diffracted/reflectedsignal unification unit 200 is thereafter compared with a detectionthreshold value that is determined in advance by a foreign matter/defectjudgment mechanism 108. The foreign matter/defect judgment mechanism 108judges that the digital data originates from the foreign matter anddefect when the digital data is greater than the threshold value andgenerates the foreign matter/defect judgment information. When theforeign matter/defect judgment information is supplied from the foreignmatter/defect judgment mechanism 108, a foreign matter/defect coordinatedetection mechanism 130 calculates the coordinate position (r, θ) of theforeign matter and defect in a main scanning direction and in asub-scanning direction from the positional information of the presentposition of main scanning and sub-scanning that are generated by theinspection object movement stage 102. When the coordinate position ofthe detected foreign matter and defect is determined, a grain sizecalculation mechanism 120 subsequently calculates the size of thedetected foreign matter and defect from the digital data group.

On the other hand, the digital data group so obtained as to correspondto each azimuth-wise detection optical system 160 is sent to thescattered/diffracted/reflected light signal unification unit 200 and atthe same time is sent to a foreign matter/defect classificationmechanism 140, too, in the form of individual digital data. The foreignmatter/defect classification mechanism 140 compares the intensities ofthe digital data of the scattering direction and judges to which of apredetermined foreign matter/defect category the detected foreign matterand defect corresponds.

As described above, the first embodiment of the invention can cope witha broad cubic angle by means of the condensation concave mirror 161using a part of its paraboloid of revolution as the reflecting surfaceand the image formation concave mirror 163 using a part of itsparaboloid of revolution as the reflecting surface.

Since the first embodiment uses the condensation concave mirror 161 andthe image formation concave mirror 163 as the reflecting mirror, asupport for holding a lens by clamping its periphery like a condenserlens is not necessary and an effective aperture area does not becomesmall.

Since the embodiment uses the conical reflecting mirrors, that is, aplurality of azimuth-wise detection optical systems produced by dividinga paraboloid of revolution mirror, the embodiment can detect reflectedlight in all azimuth directions by burying the whole periphery withoutany gap and without calling for specific lens polishing.

Since the scattered/diffracted/reflected light signal unification unit200 sums the digital data from the azimuth-wise detection optical system160 corresponding to the scattering direction designated in advanceamong a plurality of azimuth-wise detection optical systems 160, the S/Nratio can be much more improved than the S/N ratio obtained by mereaddition of the data from all the azimuth-wise detection optical systems160.

In other words, the first embodiment of the invention makes it possibleto conduct the following three (1) to (3).

(1) to acquire scattered light intensity distribution information ateach scattering azimuth angle;(2) to separate and utilize the scattered light signal from a scatteringazimuth direction advantageous for the S/N ratio; and(3) A dead angle is small at all azimuth directions and in a necessaryrange of angle of elevation at light reception cubic angles of thecondensation optical system and condensation efficiency is high.

The explanation given above primarily deals with the detection offoreign matters and defects but it would be obvious that the similareffect can be obtained when surface coarseness of the semiconductorwafer 100 as the inspection object is measured, too.

In the first embodiment described above, the light source 11 is the“pulse laser causing time-wise repeatedly the pulse oscillation of lightof the wavelength of the ultraviolet region” but lasers of thewavelengths other than the ultraviolet region may be used, too. When thecontinuously oscillating laser is used for the light source, too, thetechnology described above can be as such adapted. In the firstembodiment described above, the number of directions for isolating anddetecting the scattered/diffracted/reflected light occurring from theforeign matter and defect are the six directions of the left front/rightfront/left side/right side/left back/right back and the six azimuth-wisedetection optical systems 160 the detection direction angles of whichare spaced apart from one another by about 60 degrees are arranged.However, the merit of the azimuth-wise isolation and detection can beenjoyed when at least four directions of the front/left side/rightside/back can be detected.

In the embodiment described above, further, the focal length of thecondensation concave mirror 161 is set to be substantially equal to thefocal length of the image formation concave mirror 163 so as to form animage having substantially an equal size to the illumination spot but afocal length different from that of the condensation concave mirror 161may be given to the image formation concave mirror 163 so as to form anenlarged image of the illumination spot.

Incidentally, when the foreign matter and defect as the detection objectis extremely small and the resulting total scattered light quantity ismarkedly small, the number of photons incident into one optical detector7 drastically decreases if the total scattered light quantity is to bedivided and detected by a plurality of azimuth-wise detection opticalsystems 160. In such a case, it may be more advantages from the aspectof the S/N ratio to guide the total scattered light quantity into thesingle optical detector without isolation.

In such a case, an optical detector 8 for unified detection is disposedin addition to the optical detectors 7 corresponding to the respectiveazimuth-wise detection optical system 160 as shown in FIG. 6 so that theoptical detector 8 for unified detection and a plurality of opticaldetectors 7 can be changeably utilized.

An optical detector the light reception surface of which is greater thanthe circle having the radius given by the afore-mentioned formula I suchas a head-on type photomultiplier having a large aperture is suitablefor the optical detector 8 for unified defection. When the opticaldetector is constituted in this way, the first embodiment of theinvention makes it possible “(4) to secure the number of photonsincident into one optical detector even when the foreign matter anddefect as the detection object is extremely small and the resultingtotal scattered light quantity is markedly small”, too.

In the first embodiment of the invention described above, the number ofillumination spots formed on the surface of the inspection object is 1but it is also possible to employ the construction in which a pluralityof illumination spots are formed and scattered/diffracted/reflectedlight from each illumination spot is individually detected.

FIG. 7 shows a condensation/detection optical system according to thesecond embodiment that individually detectsscattered/diffracted/reflected light occurring from a plurality ofillumination spots.

It is possible to split light leaving a single light source into aplurality of illumination beams and to form a plurality of illuminationspots by a technology using a beam splitter or a technology using aWollaston polarizing prism for an illumination optical system.

FIG. 8 shows a construction in which light is split into twoillumination beams by the Wollaston polarizing prism 23 and twoillumination spots 3 and 4 are formed on a semiconductor wafer 100 bythe operation of an illumination lens 18.

FIG. 9 is a schematic structural view of a surface inspection apparatusfor executing a surface inspection method according to the secondembodiment of the invention.

The intensity ratio of the two illumination spots 3 and 4 and theirpolarization state can be adjusted by setting angles of a polarizer 24and a ½ wavelength plate 25. The constructions and condensation/imageformation of the scattered/diffracted/reflected light detection opticalsystem 150 and the six azimuth-wise detection optical systems 160 arethe same as those of the first embodiment described above. Therefore,explanation will be omitted.

In the second embodiment of the invention, each azimuth-wise detectionoptical system 160 forms the images of two illumination spots 3 and 4.An optical detector having two light reception sections is used for theoptical detector 7 provided to each azimuth-wise detection opticalsystem 160 and each light reception partition can detect oneillumination spot image.

The common optical axis 165 of the condensation concave mirror 161 andthe image formation concave mirror 163 constituting each azimuth-wisedetection optical system 160 is inclined outward by about 5 degrees tothe normal 167 of the surface of the inspection object in the detectiondirection to which each azimuth-wise detection optical system 160corresponds. Therefore, a point deviated from the optical axis 165 onthe surface of the inspection object in the images of the illuminationspots 3 and 4 has aberration.

To reduce this aberration, the line connecting the centers of the twolight reception sections in the optical detector 7 is arranged in such afashion as to be inclined with respect to the optical axis 165 but notorthogonal. Because the output signals can be obtained in parallel witheach other from the two light reception sections, each optical detector7 is connected to two amplifiers 26 and two A/D converters 30.

The digital data obtained from the two A/D converters 30 are synthesizedby a plural illumination signal unification units 210. When theintensity of the two illumination spots 3 and 4 is set to be equal toeach other by angle setting of the polarizer 24 and the ½ wavelengthplate 25, the S/N ratio can be improved by √{square root over (2)} timesby calculating addition mean of the two signals of the illuminationspots 3 and 4 by the plural illumination spot signal unification unit210 in comparison with the case where a single optical detector havingthe same detection sensitivity and the same noise characteristics isused.

The output digital data of this plural illumination spot signalunification unit 210 is sent to the scattered/diffracted/reflectedsignal unification unit 200. Since the subsequent functions andoperations of the scattered/diffracted/reflected signal unification unit200 are the same as those of the first embodiment, explanation in detailwill be omitted.

In addition to the advantages (1) to (4) obtained in the firstembodiment, the second embodiment provides the advantage that a higherS/N ratio can be obtained by disposing the detector capable of forming aplurality of illumination spots, isolating them, forming their imagesand detecting them individually to average a plurality ofscattered/diffracted/reflected light signals.

As described above, the invention provides the effects listed below byusing a plurality of azimuth-wise detection optical systems eachacquiring the image formation operation by a pair of two concave mirrorsusing its paraboloid of revolution as the reflecting mirror.

(1) It is possible to acquire scattered light intensity distributioninformation for each scattering direction angle.(2) The scattered light signal from the scattering direction angle thatis advantages from the aspect of the S/N ratio can be isolated andutilized.(3) The dead angles are small for all azimuth angles and within therequired range of the angle of elevation in the reception light cubicangles of the condensation optical system and condensation efficiency ishigh.(4) Even when the foreign matter and defect as the detection object isextremely small and the resulting total scattered light quantity ismarkedly small, the number of photons incident into one optical detectorcan be secured.

The invention can be established not only as the surface inspectionmethod and apparatus for semiconductor wafers, etc, but also as anazimuth-wise scattered light image formation optical apparatus for asurface inspection apparatus having a scattered/diffracted/reflectedlight detection optical system 150 and a detector 7.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A surface inspection method by irradiating light to a predeterminedposition on a surface of an inspection object to form an illuminationspot, detecting light scattered, diffracted and reflected from saidillumination spot, and detecting foreign matters and defects existing onthe surface of said inspection object or in the proximity of, andinside, the surface, said method comprising the steps of: condensing andreflecting the light scattered, diffracted and reflected from saidillumination spot by a plurality of condensation concave mirrorsarranged at a plurality of azimuth angles with respect to the surface ofsaid inspection object, respectively; reflecting light reflected fromeach of said condensation concave mirrors arranged at a predeterminedpositional relationships with each of a plurality of image formationconcave mirrors arranged at a higher angle of elevation than saidcondensation concave mirror with respect to the surface of saidinspection object for each of said plurality of azimuth angles;distinguishing and detecting light reflected by said plurality of imageformation concave mirrors; and detecting foreign matters and defectsexisting on the surface of said inspection object or in the proximityof, and inside, the surface of said inspection object on the basis ofthe light detected. 2-25. (canceled)